Strands are unwound from spools in many industrial manufacturing operations. For many of these applications it is important that the tension in the withdrawn strands remain constant during the whole process. Numerous tension control devices for regulating the withdrawal of strand material from a spool exist. Many use a simple brake with a constant brake force applied to the rotating spool. This results is an increase of the strand tension as the spool diameter decreases during the unwinding operation. Other devices employ a force-loaded dancer roll around which the strands are deflected. These dancer rolls are connected to a brake which in turn are applied to the rotating spool. More sophisticated strand tensioning systems use complex and expensive electronic means to measure the strand tension and electronically vary the applied tension with a close-loop feedback or an open-loop control system to achieve constant output tension.
The invention disclosed in this application employs a simple, mechanical tension device consisting of a movable spool-mounting, a spool-brake and a selectable loading force applied to the spool and against the spool-brake. These elements work together in such a manner as to result in constant strand-tension which is not affected by the size of the spool or the operation speed. It is in fact a mechanical, close-loop tension control system. The maintaining of constant withdraw tension at any spool-diameter can be mathematically proven.